Aqueous ink composition for ball-point pen

ABSTRACT

An aqueous ink for a ball-point pen which is stable over time and has high pigment dispersion stability, includes a pigment, a water-soluble organic solvent, water, xanthane gum of about 0.01 to about 0.2 wt. % and a sodium alginate of about 0.2 to about 0.6 wt. % of a total amount of the ink.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an aqueous ink composition for aball-point pen.

[0003] 2. Description of the Related Art

[0004] Conventionally, an aqueous ink for a ball-point pen has beendisclosed in Japanese Patent Laid-Open No. 59-74175 or Japanese PatentLaid-Open No. 59-138281.

[0005] The aqueous ink disclosed in Japanese Patent Laid-Open No.59-74175 contains xanthane gum of between 0.20 to 0.45 wt. %, and theaqueous ink disclosed in Japanese Patent Laid-Open No. 59-138281contains xanthane gum of between 0.20 to 0.45 wt. % and a permeabledrying agent of between 0.5 to 10.0 wt. %, for providing pseudoplasticoviscosity.

[0006] However, since xanthane gum is an ionic polysaccharide, when alarge amount of xanthane gum is used, it reacts with an ionic componentin the ink, preservation stability is impaired, and phenomena such asink shortage, dripping, or dripping-down occur at an ordinary (e.g.,operating) temperature for a half year to one year, resulting in writingfailure. To solve these problems, Japanese Patent Laid-Open No.6-256700, provides aqueous ink for a ball-point pen containing xanthanegum of 0.2 wt. % or less and a non-ionic polysaccharide of 0.01 to 0.5wt. %, thereby improving stability over time.

[0007] When xanthane gum and non-ionic polysaccharide are mixedtogether, ink preservation stability is improved. However, because ofnon-ionic properties of polysaccharide, when the non-ionicpolysaccharide is added, lengthy stirring must be performed to dispersethe non-ionic polysaccharide. In addition, even after the ink has beenprepared, when microscopic observation is performed to confirm thedispersion state of a pigment, there have been observed blocks of anycomponents failing to disperse. This problem leads to writing failures.

SUMMARY OF THE INVENTION

[0008] In view of the foregoing and other problems, disadvantages, anddrawbacks of the conventional aqueous ink for a ball-point pen, thepresent invention has been devised, and it is an object of the inventionto provide an aqueous ink for a ball-point pen which has high stabilityover time and high pigment dispersion stability.

[0009] The present inventors have conducted extensive research to solvethe above problems. As a result, the inventors discovered that the aboveobject could be achieved by mixing a small amount of xanthane gum and anionic polysaccharide together, and the invention is based on thisfinding.

[0010] That is, the aqueous ink for the ball-point pen of the inventionincludes a pigment, a water-soluble organic solvent, and water, and ischaracterized by containing xanthane gum of substantially about 0.01 toabout 0.2 wt. % and an ionic polysaccharide of substantially about 0.2to about 0.6 wt. % other than xanthane gum in a total quantity of theink.

[0011] Xanthane gum of about 0.01 to about 0.2 wt. % is used for theaqueous ink for the ball-point pen of the present invention. If xanthanegum exceeds about 0.2 wt. %, it reacts with an ionic polysaccharide, andthe ink preservation stability is impaired over time. Further, if thexanthane gum exceeds about 0.45 wt. %, writing properties of the aqueousink are impaired, which is not preferable.

[0012] Specifically, xanthane gum includes “Kelzan” (TradeName)(supplied by Kelco Division of Merck & Co., Ltd.) and, “Echo Gum”,“Kertrol” and “Monat Gum” (Trade Names) (supplied by DainipponPharmaceutical Co., Ltd.).

[0013] As an ionic polysaccharide, sodium alginate is preferable and itmixes well with water. Besides sodium alginate, a natural Arabic gum,casein, gelatin, carrageenan, alginic acid, semi-synthetic carboxymethylcellulose, sodium carboxyrnethylstarch, synthetic sodium polyacrylate,and/or polyacrylic acid can be used. Sodium alginate specificallyincludes “Manucol DMF” and “Manugel GMB” (commercially available fromDainippon Pharmaceutical Co., Ltd.) or the like.

[0014] Xanthane gum and an ionic polysaccharide other than xanthane gumare combined together, thereby uniformly dispersing a pigment quickly.Pigment dispersion stability and preservation stability are improved,and further, proper viscosity is achieved, thereby improving writingperformance.

[0015] If an ionic polysaccharide such as sodium alginate exceeds about0.6 wt. %, supernatant liquid is produced, which impairs writingperformance. In contrast, if an ionic polysaccharide such as sodiumalginate is less than about 0.2 wt. %, pigment stability cannot bemaintained, and color gradation is produced.

[0016] Further, if only sodium alginate is used, without combiningxanthane gum, thixotropy properties cannot be obtained. Similarly, whenonly using xanthane gum of about 0.2 wt. % or less, without combining anionic polysaccharide, pigment stability cannot be maintained, and colorgradation is produced.

[0017] However, when xanthane gum of about 0.01 to about 0.2 wt. % andan ionic polysaccharide, such as sodium alginate of about 0.2 to about0.6 wt. %, are combined together, an ink can be produced having superiorstability over time, superior pigment dispersion properties, and properviscosity. Incidentally, when the content of xanthane gum in the ink isless than about 0.01 wt. %, thixotropy properties cannot be obtained.The relationship of varying combinations of xanthane gum and an ionicpolysaccharide, such as sodium alginate, on the quality and propertiesof the ink is shown in Table 1 below. TABLE 1 Combination of Components(wt %) Ink Large amount of xanthanegum only Poor writing performance(more than about 0.45 wt. %) Only xanthane gum (about 0.2 to Poorstability over time 0.45 wt. %) Small amount of xanthane gum onlyPigment stability cannot be (less than about 0.2 wt. %) maintained, andcolor gradation is produced Xanthane gum (about 0.01 to about 0.2 Poorwriting performance and wt. %) and sodium alginate of more supernatantliquid produced than 0.6 wt. % Xanthane gum (about 0.01 to about 0.2Good stability with an elapse of wt. %) and sodium alginate (about 0.2time, good pigment dispersion to about 0.6 wt. %) properties, and properviscosity Xanthane gum (about 0.01 to about 0.2 Pigment stability cannotbe wt. %) and sodium alginate (less than maintained, and color gradationabout 0.2 wt. %) is produced Xanthane gum (less than about 0.01Thixotropy properties cannot be wt. %) and sodium alginate obtained Onlysodium alginate Thixotropy properties cannot be obtained

[0018] As a pigment, there can be used any of inorganic and organicpigments routinely used in conventional aqueous ink compositions withoutbeing limited thereto. The inorganic pigment may include titanium oxide,carbon black, metal powder or the like, for example. Further, theorganic pigment may include azo-lake, insoluble azo-pigment, chelateazo-pigment, phthalocyanine pigment, perylene and perinone pigments,anthraquinone pigment, quinacridone pigment, lake pigment, nitropigment, nitroso-pigment or the like.

[0019] Specifically, there are exemplified Phthalocyanine Blue (C. I.74160), Phthalocyanine Green (C. I. 74260), Hansa Yellow 3G (C. I.11670), Disazoyellow GR (C. I. 21100), Permanent Red 4R (C. I. 12335),Brilliant Carmin 6B (C. I. 15850), Quinacridone Red (C. I. 46500) orsimilar colors.

[0020] These pigments may be employed singly, or used in anycombination. The pigment content of a total amount of the ink isgenerally substantially within the range of about 4 to about 12 wt. %,and is preferably within the range of about 6 to about 8 wt. %. Ifpigment content exceeds 12 wt. %, dispersion properties are inferior,which is not preferable.

[0021] As a water-soluble organic solvent, there can be used glycerin,diglycerin, ethylene glycol, diethylene glycol, tridiethylene glycol,propylene glycol, polyethylene glycol, polypropylene glycol,thiodiglycol, 1-3-butylene glycol, 2-pyrrolidone,n-methyl-2-pyrrolidone, dimethylformamide, dimethylimidazolidinone orthe like, singly or in combination. If ethylene glycol is used as one ofwater-soluble organic solvent and a content of ethylene glycol is notless than about 11 wt. %, cap-off property which is a property ofretaining writability for a prolonged period of time with the capremoved from the pen, can be improved.

[0022] The water content of a total amount of the ink is set to about 35to 49 wt. %, which is less than that used in a conventional aqueous inkfor a ball-point pen. In this manner, an ink which is close to anoil-based ink is produced, thus making it possible to obtain smoothwriting performance. In addition, the ball of the ball-point pen tip ishardly corroded. When a metallic pigment is used, an occurrence ofhydrogen can be restricted.

[0023] Further, the ink according to the present invention may containan antiseptic agent, a pH adjuster, an anti-corrosion agent, and/or adispersion agent as required. A surface active agent may be present inthe ink to benefit smooth rotation of the ball of the ball-point pentip.

[0024] The antiseptic agent includes at least one of phenol, isopropylmethyl phenol, penta chlorophenol sodium, benzoic acid, sodium benzoate,dehydroacetic acid, sodium dehydroacetate, sorbic acid, potassiumsorbate, 2-pyridinethiol-1 oxide sodium salt,1,2-benzoisothiazoline-3-one, 5-chlor-2-methyl-4-isothizoline- 3-one,2,4-thiazolybenzimidazole, p-hydroxybenzoate ester or the like.

[0025] The pH adjuster includes amine or chloride. For example, any oneor more of a variety of organic amines could be used such as monoethanolamine, diethanol amine, triethanol amine or the like, sodium hydroxide,lithium hydroxide, potassium hydroxide, sodium tripolyphosphate, sodiumcarbonate, urea, ammonia or the like.

[0026] The anti-corrosion agent includes at least one of tolyltriazole,benzotriazole and its derivatives, fatty acid phosphorous derivatives,such as octyl phosphate, dioctyl thiophosphate, imidazole,benzoimidazole and its derivative, 2-mercaptobenzothiazole, octylmethane sulfonic acid, dicyclohexyl ammonium nitrate, diisopropylammonium nitrate, propargyl alcohol, dialkylthio urea or the like.

[0027] The dispersion agent includes a water-soluble agent such asstyrene-acrylic resin dispersing agent and styrene-maleic acid resindispersing agent. The surface active agent includes at least one ofpotassium linoleic acid, potassium oleate, sodium oleate, polyoxyethylene alkylether phosphate, polyoxy ethylene alkyl phenyl ether,polyoxy ethylene lanolin or the like.

[0028] The present disclosure relates to subject matter contained inJapanese Patent Application No. Hei 11-71712, filed Mar. 17, 1999, andJapanese Patent Application No. Hei 11-223113, filed Aug. 5, 1999, andwhich are expressly incorporated herein by reference in its entirety.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, referring to the Examples provided, there are shownpreferred embodiments of the present invention. TABLE 2 ComparativeExamples Examples (wt. %) (wt. %) Component Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex.5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 11 1 2 3 Pigment Black Blue RedBlack Blue Red Green Black Blue Red Green Black Blue Red DispersedPigment Pigment Pigment Pigment Pigment Pigment Pigment Pigment PigmentPigment Pigment Pigment Pigment Pigment Solution Pigment 6.0 6.0 6.0 6.06.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 Glycerin 8.5 8.5 8.5 8.5 8.5 8.58.5 8.5 8.5 8.5 8.5 8.5 8.5 8.5 Ethylene 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.04.0 4.0 4.0 4.0 4.0 4.0 Glycol Water 30.0 30.0 30.0 30.0 30.0 30.0 30.030.0 30.0 30.0 30.0 30.0 30.0 30.0 Styrene- 1.5 1.5 1.5 1.5 1.5 1.5 1.51.5 1.5 1.5 1.5 1.5 1.5 1.5 Acrylic {open oversize brace} ResinDispersing Agent (or Styrene- Maleic Acid Resin Dispersing Agent)Xanthane Gum 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.150.15 0.15 Sodium 0.6 0.6 0.7 0.6 0.6 0.7 0.7 0.3 0.3 0.3 0.3 — — —Alginate Glycerin 20.75 20.75 20.65 21.16 21.16 21.06 20.0 21.16 21.1621.06 20.0 21.35 21.35 21.35 Anticorrosion 0.5 0.5 0.5 0.09 0.09 0.090.09 0.09 0.09 0.09 0.09 0.5 0.5 0.5 Agent (Bnzotriazole) Antiseptic 1.01.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Agent (1,2-benzoisothia- zoline- 3-one) pH Adjuster 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.08.0 8.0 8.0 8.0 8.0 8.0 (Triethanol- amine) Surface Active 3.0 3.0 3.03.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Agent (Potassium Oleate)Ion-Exchange 16.0 16.0 16.0 9.0 9.0 9.0 8.06 9.0 9.0 9.0 8.06 16.0 16.016.0 Water Ethylene — — — 7.0 7.0 7.0 9.0 7.3 7.3 7.4 9.4 — — — Glycol

[0030] In any of the Examples 1-3, a glycerin, a benzotriazole, anantiseptic agent (1,2-benzoisothiazoline-3-one), pH adjuster (triethanolamine), and a surface active agent (potassium oleate) were poured into abeaker, and were stirred for 5 minutes at 1000 rpm. Ion exchange water,xanthane gum, and sodium alginate were added, and were stirred for 2hours at 1000 rpm. Then, pigment dispersed solution was added to thissolution, and was stirred for 1 hour at 1000 rpm. Similarly, in any ofthe Examples 4-11, glycerin, benzotriazole, an antiseptic agent(1,2-benzoisothiazoline-3-one), pH adjuster (triethanol amine), asurface active agent (potassium oleate) and ethylene glycol were pouredinto a beaker, and were stirred for 5 minutes at 1000 rpm. Ion exchangewater, xanthane gum, and sodium alginate were added, and were stirredfor 2 hours at 1000 rpm. Then, pigment dispersed solution was added tothis solution, and was stirred for 1 hour at 1000 rpm. Each ofComparative Examples 1-3 was prepared in the same manner as each of theExamples 1-3 was done, except that sodium alginate was not added.

[0031] According to Examples 1 through 11, a good ink was obtained, andno change occurred while the ink was preserved (for 16 weeks) in athermostat vessel (e.g., at about 50° C. (122° F.) ). In each of theComparative Examples, pigment stability was not maintained, and colorgradation was produced.

[0032] In addition, Examples 4 to 11 show good cap-off property becausethey contain comparatively more ethylene glycol (not less than 11 wt. %)and less water than the other Examples and the Comparative Examples.Examples 1 11 were filled with an ink tank of ball-point pens and weretested to determine how long the pens can last with the cap removed fromthe pen. Examples 1 to 3 indicated that the average length of time thepens lasted was 14 days, while Examples 4 to 11 indicated that theaverage length of time the pens lasted was 21 days. Good cap-offproperty can be obtained in Examples 4 to 11.

[0033] Generally, when the amount of water-soluble solvent, exceptwater, is increased, ink on a paper dries more slowly and tends totransfer easily to a stacked sheet. However, when a portion of water isreplaced with ethylene glycol, the ink permeates paper rapidly and tendsto be prevented from transferring to other sheets. When water isdecreased and ethylene glycol is increased, this transferring problemcan be eliminated and the cap-off property can be improved as describedabove.

[0034] As described above, according to the present invention, anaqueous ink for a ball-point pen is provided having improved viscosityand high stability over time by mixing a small amount of xanthane gumand ionic polysaccharide. Further, a pigment can be dispersed finely anduniformly within a short time period, and the aqueous ink for theball-point pen with high pigment dispersion stability can be provided.

[0035] While the invention has been described in terms of severalpreferred embodiments, those skilled in the art will recognize that theinvention can be practiced with modification within the spirit and scopeof the appended claims.

Having thus described our invention, what we claim as new and desire tosecure by letters patent is as follows:
 1. An aqueous ink for aball-point pen, comprising: a pigment; a water-soluble organic solvent;and water, wherein said aqueous ink comprises xanthane gum ofsubstantially about 0.01 to about 0.2 wt. % and an ionic polysaccharideof substantially about 0.2 to about 0.6 wt. %, other than xanthane gum,in a total amount of the ink.
 2. The aqueous ink as claimed in claim 1 ,wherein said ionic polysaccharide, other than xanthane gum, comprises asodium alginate.
 3. The aqueous ink as claimed in claim 1 , wherein awater content is substantially about 35 to about 49 wt. % in the totalamount of the ink.
 4. The aqueous ink as claimed in claim 2 , wherein awater content is substantially about 35 to about 49 wt. % in the totalamount of the ink.
 5. The aqueous ink as claimed in claim 1 , whereinsaid ionic polysaccharide, other than xanthane gum, is at least onesubstance selected from the group consisting of a natural Arabic gum,casein, gelatin, carrageenan, alginic acid, semi-synthetic carboxymethylcellulose, sodium caboxymethylstarch, synthetic sodium polyacrylate, andpolyacrylic acid.
 6. The aqueous ink as claimed in claim 3 , whereinsaid ionic polysaccharide, other than xanthane gum, is at least onesubstance selected from the group consisting of a natural Arabic gum,casein, gelatin, carrageenan, alginic acid, semi-synthetic carboxymethylcellulose, sodium carboxymethylstarch, synthetic sodium polyacrylate,and polyacrylic acid.
 7. The aqueous ink as claimed in claim 1 , whereinsaid pigment comprises an inorganic pigment.
 8. The aqueous ink asclaimed in claim 2 , wherein said pigment comprises an inorganicpigment.
 9. The aqueous ink as claimed in claim 1 , wherein said pigmentcomprises an organic pigment.
 10. The aqueous ink as claimed in claim 2, wherein said pigment comprises an organic pigment.
 11. The aqueous inkas claimed in claim 7 , wherein said inorganic pigment is at least onesubstance selected from the group consisting of titanium oxide, carbonblack, and metal powder.
 12. The aqueous ink as claimed in claim 8 ,wherein said inorganic pigment is at least one substance selected fromthe group consisting of titanium oxide, carbon black, and metal powder.13. The aqueous ink as claimed in claim 9 , wherein said organic pigmentis at least one substance selected from the group consisting ofazo-lake, insoluble azo-pigment, chelate azo-pigment, phthalocyaninepigment, perylene and perinone pigments, anthraquinone pigment,quinacridone pigment, lake pigment, nitro pigment, and nitroso-pigment.14. The aqueous ink as claimed in claim 10 , wherein said organicpigment is at least one substance selected from the group consisting ofazo-lake, insoluble azo-pigment, chelate azo-pigment, phthalocyaninepigment, perylene and perinone pigments, anthraquinone pigment,quinacridone pigment, dye-rake, nitro pigment, and nitroso-pigment. 15.The aqueous ink as claimed in claim 1 , wherein a content of saidpigment is substantially within the range of about 4 to about 12 wt. %.16. The aqueous ink as claimed in claim 15 , wherein a content of saidpigment is substantially within the range of about 6 to about 8 wt. %.17. The aqueous ink as claimed in claim 2 , wherein a content of saidpigment content is substantially within the range of about 4 to about 12wt. %.
 18. The aqueous ink as claimed in claim 17 , wherein a content ofsaid pigment is substantially within the range of about 6 to about 8 wt.%.
 19. The aqueous ink as claimed in claim 1 , wherein saidwater-soluble organic solvent is at least one substance selected fromthe group comprising glycerin, diglycerin, ethylene glycol, diethyleneglycol, tridiethylene glycol, propylene glycol, polyethylene glycol,polypropylene glycol, thiodiglycol, 1-3-butylene glycol, 2-pyrrolidone,n-methyl-2-pyrrolidone, dirnethylformamide, and dimethylimidazolidinone.20. The aqueous ink as claimed in claim 2 , wherein said water-solubleorganic solvent is at least one substance selected from the groupconsisting of glycerin, diglycerin, ethylene glycol, diethylene glycol,tridiethylene glycol, propylene glycol, polyethylene glycol,polypropylene glycol, thiodiglycol, 1-3-butylene glycol, 2-pyrrolidone,n-methyl-2-pyrrolidone, dimethylformamide, and dimethylimidazolidinone.21. The aqueous ink as claimed in claim 1 , further including at leastone of a surface active agent, an antiseptic agent, a pH adjuster, ananticorrosion agent, and a dispersion agent.
 22. The aqueous ink asclaimed in claim 2 , further including at least one of a surface activeagent, an antiseptic agent, a pH adjuster, an anticorrosion agent, and adispersion agent.
 23. The aqueous ink according to claim 21 , whereinsaid pH adjuster includes at least one of monoethanol amine, diethanolamine, triethanol amine, sodium hydroxide, lithium hydroxide, potassiumhydroxide, sodium tripolyphosphate, sodium carbonate, urea, and ammonia.24. The aqueous ink according to claim 21 , wherein said anti-corrosionagent includes at least one of tolyltriazole, benzotriazole and itsderivatives, fatty acid phosphorous derivatives, such as octylphosphate, dioctyl thiophosphate, imidazole, benzoimidazole and itsderivative, 2-mercaptobenzothiazole, octyl methane sulfonic acid,dicyclohexyl ammonium nitrate, diisopropyl ammonium nitrate, propargylalcohol, and dialkylthio urea.
 25. The aqueous ink according to claim 21, wherein said antiseptic agent includes at least one phenol, isopropylmethyl phenol, penta chlorophenol sodium, benzoic acid, sodium benzoate,dehydroacetic acid, sodium dehydroacetate, sorbic acid, potassiumsorbate, 2-pyridinethiol-1 oxide sodium salt,1,2-benzoisothiazoline-3-one, 5-chlor-2-methyl-4-isothizoline- 3-one,one, 2,4-thiazolylbenzimidazole, and p-hydroxybenzoate ester.
 26. Theaqueous ink according to claim 21 , wherein said surface active agentincludes at least one of potassium linoleic acid, potassium oleate,sodium oleate, polyoxy ethylene alkylether phosphate, polyoxy ethylenealkyl phenyl ether, and polyoxy ethylene lanolin.
 27. The aqueous inkaccording to claim 1 , wherein said water-soluble organic solventcomprises ethylene glycol and a content of said ethylene glycol issubstantially not less than about 11 wt. %.
 28. The aqueous inkaccording to claim 2 , wherein said water-soluble organic solventcomprises ethylene glycol and a content of said ethylene glycol issubstantially not less than about 11 wt. %.